Variable magnification optical system, optical apparatus, and method for producing variable magnification optical system

ABSTRACT

A variable magnification optical system comprising, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a rear lens group having negative refractive power; upon varying a magnification from a wide angle end state to a tele photo end state, a distance between the first lens group and the second lens group being varied, a distance between the second lens group and the third lens group being varied, and a distance between the third lens group and the rear lens group being varied; the third lens group or the rear lens group comprising a focusing lens group which is moved upon carrying out focusing from an infinitely distant object to a closely distant object; and predetermined conditional expression(s) being satisfied, thereby various aberrations being corrected superbly.

TECHNICAL FIELD

The present invention relates to a variable magnification optical system, an optical apparatus and a method for manufacturing the variable magnification optical system.

BACKGROUND ART

There has been proposed a variable magnification optical system that is small in size but can adopt large-sized image pick-up device suitable for photo-taking a motion picture and for effecting high speed focusing. For example, refer to Japanese Patent application Laid-Open Gazette No. 2015-064492. However, in the conventional variable magnification optical system, corrections of various aberrations have not been made sufficiently.

PRIOR ART REFERENCE Patent Document

-   Patent Document 1: Japanese Patent application -   Laid-Open Gazette No. 2015-064492.

SUMMARY OF THE INVENTION

The present invention is related to a variable magnification optical system comprising, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a rear lens group having negative refractive power;

upon varying a magnification, a distance between said first lens group and said second lens group being varied, a distance between said second lens group and said third lens group being varied, and a distance between said third lens group and said rear lens group being varied;

said third lens group or said rear lens group comprising a focusing lens group which is moved upon carrying out focusing; and

the following conditional expressions being satisfied:

2.00 < f 1/fw < 8.000 0.400 < BFw/fw < 1.300

where f1 denotes a focal length of said first lens group, fw denotes a focal length of said variable optical system in a wide angle end state, BFw denotes a back focus of said variable magnification optical system in the wide angle end state, and fw denotes the focal length of said variable magnification optical system in the wide angle end state.

Further, the present invention is related to a method for manufacturing a variable magnification optical system comprising, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a rear lens group having negative refractive power; comprising the steps of:

constructing such that, upon varying a magnification, a distance between said first lens group and said second lens group is varied, a distance between said second lens group and said third lens group is varied, and a distance between said third lens group and said rear lens group is varied;

constructing such that said third lens group or said rear lens group comprises a focusing lens group which is moved upon carrying out focusing; and

constructing such that the following conditional expressions are satisfied:

2.00 < f 1/fw < 8.000 0.400 < BFw/fw < 1.300

where f1 denotes a focal length of said first lens group, fw denotes a focal length of said variable optical system in a wide angle end state, BFw denotes a back focus of said variable magnification optical system in the wide angle end state, and fw denotes the focal length of said variable magnification optical system in the wide angle end state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A, FIG. 1B and FIG. 1C are cross sectional views in the wide angle end state, in the intermediate focal length state and in the telephoto end state, respectively, of a variable magnification optical system according to a First Example.

FIG. 2A, FIG. 2B and FIG. 2C are graphs showing various aberrations, upon focusing on an infinite distance object, in the wide angle end state, in the intermediate focal length state, and in the telephoto end state, respectively, of the variable magnification optical system according to the First Example.

FIG. 3A, FIG. 3B and FIG. 3C are graphs showing various aberrations, upon focusing on a close distance object, in the wide angle end state, in the intermediate focal length state, and in the telephoto end state, respectively, of the variable magnification optical system according to the First Example.

FIG. 4A, FIG. 4B and FIG. 4C are cross sectional views in the wide angle end state, in the intermediate focal length state and in the telephoto end state, respectively, of a variable magnification optical system according to a Second Example.

FIG. 5A, FIG. 5B and FIG. 5C are graphs showing various aberrations, upon focusing on an infinite distance object, in the wide angle end state, in the intermediate focal length state, and in the telephoto end state, respectively, of the variable magnification optical system according to the Second Example.

FIG. 6A, FIG. 6B and FIG. 6C are graphs showing various aberrations, upon focusing on a close distance object, in the wide angle end state, in the intermediate focal length state and in the telephoto end state, respectively, of the variable magnification optical system according to the Second Example.

FIG. 7A, FIG. 7B and FIG. 7C are cross sectional views in the wide angle end state, in the intermediate focal length state and in the telephoto end state, respectively, of a variable magnification optical system according to a Third Example.

FIG. 8A, FIG. 8B and FIG. 8C are graphs showing various aberrations, upon focusing on an infinite distance object, in the wide angle end state, in the intermediate focal length state and in the telephoto end state, respectively, of the variable magnification optical system according to the Third Example

FIG. 9A, FIG. 9B and FIG. 9C are graphs showing various aberrations, upon focusing on a close distance object, in the wide angle end state, in the intermediate focal length state and in the telephoto end state, respectively, of the variable magnification optical system according to the Third Example.

FIG. 10A, FIG. 10B and FIG. 10C are cross sectional views in the wide angle end state, in the intermediate focal length state and in the telephoto end state, respectively, of a variable magnification optical system according to a Fourth Example.

FIG. 11A, FIG. 11B and FIG. 11C are graphs showing various aberrations, upon focusing on an infinite distance object, in the wide angle end state, in the intermediate focal length state and in the telephoto end state, respectively, of the variable magnification optical system according to the Fourth Example.

FIG. 12A, FIG. 12B and FIG. 12C are graphs showing various aberrations, upon focusing on a close distance object, in the wide angle end state, in the intermediate focal length state and in the telephoto end state, respectively, of the variable magnification optical system according to the Fourth Example.

FIG. 13A, FIG. 13B and FIG. 13C are cross sectional views in the wide angle end state, in the intermediate focal length state and in the telephoto end state, respectively, of a variable magnification optical system according to a Fifth Example.

FIG. 14A, FIG. 14B and FIG. 14C are graphs showing various aberrations, upon focusing on an infinite distance object, in the wide angle end state, in the intermediate focal length state and in the telephoto end state, respectively, of the variable magnification optical system according to the Fifth Example

FIG. 15A, FIG. 15B and FIG. 15C are graphs showing various aberrations, upon focusing on a close distance object, in the wide angle end state, in the intermediate focal length state and in the telephoto end state, respectively, of the variable magnification optical system according to the Fifth Example.

FIG. 16 is a view showing a configuration of a camera equipped with the variable magnification optical system.

FIG. 17 is a flowchart schematically showing a method for manufacturing the variable magnification optical system.

EMBODIMENT FOR CARRYING OUT THE INVENTION

Hereinafter, a variable magnification optical system according to the present embodiment, an optical apparatus and a method for producing the variable magnification optical system, will be explained. At first, the variable magnification optical system according to the present embodiment will be explained.

The variable magnification optical system according to the present embodiment comprises, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a rear lens group having negative refractive power;

upon varying a magnification from a wide angle end state to a telephoto end state, a distance between said first lens group and said second lens group being varied, a distance between said second lens group and said third lens group being varied, and a distance between said third lens group and said rear lens group being varied;

said third lens group or said rear lens group comprising a focusing lens group which is moved upon carrying out focusing from an infinite distance object to a close distance object; and

the following conditional expressions (1) and (2) being satisfied:

$\begin{matrix} {2.00 < {f\; 1\text{/}{fw}} < 8.000} & (1) \\ {0.400 < {{BFw}\text{/}{fw}} < 1.300} & (2) \end{matrix}$

where f1 denotes a focal length of said first lens group, fw denotes a focal length of said variable optical system in a wide angle end state, BFw denotes a back focus of said variable magnification optical system in a wide angle end state, and fw denotes the focal length of said variable magnification optical system in the wide angle end state.

The rear lens group of the variable magnification optical system according to the present embodiment comprises at least one lens group. Meanwhile, in the present embodiment, a lens group means a portion which comprises at least one lens separated by an air space. Further, in the present embodiment, a lens component means a single lens or a cemented lens composed of two or more lenses cemented with each other.

The variable magnification optical system according to the present embodiment can conduct superbly aberration corrections upon varying a magnification, by varying respective distances between the lens groups upon varying magnification from a wide angle end state to a telephoto end state. Further, the focusing lens group may be made small in size and reduced in weight by disposing the focusing lens group in the third lens group or in the rear lens group, and as a result, high speed focusing becomes possible and the variable magnification optical system and the lens barrel can be small-sized.

The conditional expression (1) defines a ratio of a focal length of the first lens group to a focal length of the variable optical system in the wide angle end state. With satisfying the conditional expression (1), the variable magnification optical system according to the present embodiment can correct superbly coma aberration and other various aberrations in the wide angle end state.

When the value of f1/fw is equal to or exceeds the upper limit of the conditional expression (1), refractive power of the first lens group becomes small, and it becomes difficult to correct superbly various aberrations in the wide angle end state. Meanwhile, in order to secure the advantageous effect of the present embodiment more surely, it is preferable to set the upper limit value of the conditional expression (1) to 7.000. Further, in order to secure the advantageous effect of the present embodiment much more surely, it is preferable to set the upper limit value of the conditional expression (1) to 6.500, and much more preferable to 6.300.

On the other hand, when the value of f1/fw is equal to or falls below the lower limit of the conditional expression (1), refractive power of the first lens group becomes large, and it becomes difficult to correct superbly various aberrations in the wide angle end state, and in particular, coma aberration. Meanwhile, in order to secure the advantageous effect of the present embodiment more surely, it is preferable to set the lower limit value of the conditional expression (1) to 3.00. In order to secure the advantageous effect of the present-embodiment much more surely, it is preferable to set the lower limit value of the conditional expression (1) to 4.00 and more preferable to 4.50.

The conditional expression (2) defines a ratio of a back focus of the variable magnification optical system in the wide angle end state to a focal length of the variable magnification optical system in the wide angle end state.

With satisfying the conditional expression (2), the variable magnification optical system according to the present embodiment can correct superbly a coma aberration and other various aberrations in the wide angle end state. Meanwhile, by the term “back focus” is meant a distance from the most image side lens surface to the image plane on the optical axis.

When the value of BFw/fw is equal to or exceeds the upper limit of the conditional expression (2), the back focus of the variable magnification optical system in the wide angle end state relative to the focal length of the variable magnification optical system in the wide angle end state becomes large and it becomes difficult to correct superbly various aberrations in the wide angle end state. Meanwhile, in order to attain the advantageous effect of the present embodiment more surely, it is preferable to set the upper limit value of the conditional expression (2) to 1.000. Further, in order to attain the advantageous effect of the present embodiment much more surely, it is preferable to set the upper limit value of the conditional expression (2) to 0.950 and much more preferable to 0.900.

On the other hand, when the value of BFw/fw is equal to or falls below the lower limit of the conditional expression (2), the back focus of the variable magnification optical system in the wide angle end state relative to the focal length of the variable magnification optical system in the wide angle end state becomes small, and it becomes difficult to correct various aberrations in the wide angle end state, and in particular coma aberration superbly. Meanwhile, in order to secure the advantageous effect of the present embodiment more surely, it is preferable to set the lower limit value of the conditional expression (2) to 0.500. In order to secure the advantageous effect of the present embodiment much more surely, it is preferable to set the lower limit value of the conditional expression (2) to 0.600 and more preferable to 0.650.

Incidentally, in the conditional expression (2), “back focus of the variable magnification optical system in the wide angle end state” denoted by BFw may be replaced by “back focus of the variable magnification optical system in the state where the whole length is smallest”, and “focal length of the variable magnification optical system in the wide angle end state” denoted by fw may be replaced by “focal length of the variable magnification optical system in the state where the whole length is smallest”. That is to say, the conditional expression (2) may be expressed, as below:

$\begin{matrix} {0.400 < {{BFs}\text{/}{fs}} < 1.300} & (2) \end{matrix}$ where BFs denotes a back focus of said variable magnification optical system in a state where the whole length is smallest, and fs denotes a focal length of said variable magnification optical system in the state where the whole length is smallest.

By the above-mentioned configuration, the variable magnification optical system according to the present embodiment can be small-sized but be made compatible with a large sized imaging device, and it is possible to realize a variable magnification optical system which can correct various aberrations superbly upon varying magnification and upon carrying out focusing.

In the variable magnification optical system according to the present embodiment, it is desirable that the following conditional expression (3) is satisfied:

$\begin{matrix} {0.500 < {1\text{/}\beta\;{Rw}} < 1.200} & (3) \end{matrix}$ where βRw denotes transverse magnification of the lens group disposed on the most image plane side in the wide angle end state.

The conditional expression (3) defines the transverse magnification of the lens group disposed on the most image plane side in the wide angle end state. With satisfying the conditional expression (3), the variable magnification optical system according to the present embodiment can correct superbly astigmatism and other various aberrations in the wide angle end state.

When the value of 1/βRw is equal to or exceeds the upper limit value of the conditional expression (3) of the variable magnification optical system according to the present embodiment, the transverse magnification of the lens group disposed on the most image plane side in the wide angle end state, becomes small, and it becomes difficult to correct superbly various aberrations in the wide angle end state and, in particular, astigmatism. Meanwhile, in order to secure the advantageous effect of the present embodiment more surely, it is preferable to set the upper limit value of the conditional expression (3) to 1.100. Further, in order to secure the advantageous effect of the present embodiment much more surely, it is preferable to set the upper limit value of the conditional expression (3) to 1.000, and more preferable to 0.900.

On the other hand, when the value of 1/βRw in the conditional expression (3) of the variable magnification optical system according to the present embodiment, is equal to or falls below the lower limit value, the transverse magnification of the lens group disposed on the most image plane side in the wide angle end state, becomes large, and curvature of field in the wide angle end state is apt to be generated, and further it becomes difficult to correct superbly various aberrations. Meanwhile, in order to secure the advantageous effect of the variable magnification optical system according to the present embodiment more surely, it is preferable to set the lower limit value of the conditional expression (3) to 0.550. And in order to secure the advantageous effect of the present embodiment much more surely, it is preferable to set the lower limit value of the conditional expression (3) to 0.580, and more preferable to 0.600.

Further, in the variable magnification optical system according to the present embodiment, it is desirable that the following conditional expression (4) is satisfied:

$\begin{matrix} {4.000 < {f\; 1\text{/}f\; 1{Rw}} < 9.000} & (4) \end{matrix}$ where f1 denotes the focal length of the first lens group, and f1Rw denotes a composite focal length of lens groups in the wide angle end state disposed on the side which is closer to the image plane than the first lens group.

The conditional expression (4) defines a ratio of the focal length of the first lens group to the composite focal length of lens groups in the wide angle end state disposed on the side which is closer to the image plane than the first lens group. With satisfying the conditional expression (4), the variable magnification optical system according to the present embodiment can correct superbly coma aberration and other various aberrations in the wide angle end state. Further, with satisfying the conditional expression (4), variations in spherical aberration and in other various aberrations can be suppressed upon varying magnification from the wide angle end state to the telephoto end state.

When the value of f1/f1Rw is equal to or exceeds the upper limit value of the conditional expression (4) of the variable magnification optical system according to the present embodiment, refractive power of the lens groups in the wide angle end state disposed on the side which is closer to the image plane than the first lens group, becomes large, and it becomes difficult to correct superbly various aberrations in the wide angle end state and, in particular, coma aberration. Further, upon varying magnification from the wide angle end state to the telephoto end state, it becomes difficult to suppress variations in spherical aberration and in other various aberrations. Meanwhile, in order to secure the advantageous effect of the present embodiment more surely, it is preferable to set the upper limit value of the conditional expression (4) to 8.500. Further, in order to secure the advantageous effect of the present embodiment much more surely, it is preferable to set the upper limit value of the conditional expression (4) to 8.000, and more preferable to 7.000.

On the other hand, when the value of f1/f1Rw in the conditional expression (4) of the variable magnification optical system according to the present embodiment, is equal to or falls below the lower limit value, refractive power of the first lens group becomes large, and it becomes difficult to correct various aberrations in the wide angle end state and in particular, coma aberration. Further, upon varying magnification from the wide angle end state to the telephoto end state, it becomes difficult to suppress variations in spherical aberration and in other various aberrations. Meanwhile, in order to secure the advantageous effect of the variable magnification optical system according to the present embodiment more surely, it is preferable to set the lower limit value of the conditional expression (4) to 5.000. And in order to secure the advantageous effect of the present embodiment much more surely, it is preferable to set the lower limit value of the conditional expression (4) to 5.100, and more preferable to 5.200.

Further, in the variable magnification optical system according to the present embodiment, it is desirable that the following conditional expression (5) is satisfied:

$\begin{matrix} {{{nd}\; 3{fp}} < 1.800} & (5) \end{matrix}$ where nd3fp denotes refractive index of a lens having the largest refractive index in the third lens group.

The conditional expression (5) defines refractive index of the lens having the largest refractive index in the third lens group. With using glass material having high refractive index satisfying the conditional expression (5), the variable magnification optical system according to the present embodiment can correct superbly longitudinal chromatic aberration and spherical aberration.

When the value of nd3fp is equal to or exceeds the upper limit value of the conditional expression (5) of the variable magnification optical system according to the present embodiment, refractive power of the third lens group becomes large, and it becomes difficult to correct superbly longitudinal chromatic aberration and spherical aberration. Meanwhile, in order to secure the advantageous effect of the present embodiment more surely, it is preferable to set the upper limit value of the conditional expression (5) to 1.750. Further, in order to secure the advantageous effect of the present embodiment much more surely, it is preferable to set the upper limit value of the conditional expression (5) to 1.700, and more preferable to 1.650.

In the variable magnification optical system according to the present embodiment, it is desirable that the following conditional expression (6) is satisfied:

$\begin{matrix} {50.000 < {{vd}\; 3p}} & (6) \end{matrix}$ where νd3p denotes Abbe's number of a lens having the smallest Abbe's number in the third lens group.

The conditional expression (6) defines the Abbe's number of a lens having the smallest Abbe's number in the third lens group. With using glass material of low dispersion satisfying the conditional expression (6), the variable magnification optical system according to the present embodiment can let the third lens group have anomalous dispersion, and it becomes possible to correct superbly longitudinal chromatic aberration and spherical aberration.

When the value of νd3p in the conditional expression (6) of the variable magnification optical system according to the present embodiment, is equal to or falls below the lower limit value, it is not possible to let the third lens group have sufficient anomalous dispersion, and it becomes difficult to correct superbly longitudinal chromatic aberration and spherical aberration. Meanwhile, in order to secure the advantageous effect of the present embodiment more surely, it is preferable to set the lower limit value of the conditional expression (6) to 55.000. And, in order to secure the advantageous effect of the present embodiment much more surely, it is preferable to set the lower limit value of the conditional expression (6) to 58.000, and more preferable to 60.000.

Further, in the variable magnification optical system according to the present embodiment, it is desirable that the following conditional expression (7) is satisfied:

$\begin{matrix} {1.100 < {\beta\;{Fw}} < 2.500} & (7) \end{matrix}$ where βFw denotes a transverse magnification of the focusing lens group in the wide angle end state.

The conditional expression (7) defines the transverse magnification of the focusing lens group in the wide angle end state. With satisfying the conditional expression (7), the variable magnification optical system according to the present embodiment can make an amount of movement of the focusing lens group upon focusing small so that the variable magnification optical system can be made small-sized.

When the value of βFw is equal to or exceeds the upper limit value of the conditional expression (7) of the variable magnification optical system according to the present embodiment, the amount of movement of the focusing lens group upon focusing becomes large, so it becomes difficult to make the variable magnification optical system small-sized. Meanwhile, in order to secure the advantageous effect of the present embodiment more surely, it is preferable to set the upper limit value of the conditional expression (7) to 2.000. Further, in order to secure the advantageous effect of the present embodiment much more surely, it is preferable to set the upper limit value of the conditional expression (7) to 1.800, and more preferable to 1.700.

On the other hand, when the value of βFw in the conditional expression (7) of the variable magnification optical system according to the present embodiment, is equal to or falls below the lower limit value, the amount of movement of the focusing lens group upon focusing becomes small, so it becomes difficult to control focusing. Meanwhile, in order to secure the advantageous effect of the present embodiment more surely it is preferable to set the lower limit value of the conditional expression (7) to 1.200. Further, in order to secure the advantageous effect of the present embodiment much more surely, it is preferable to set the upper limit value of the conditional expression (7) to 1.250 and more preferable to 1.300.

Further, in the variable magnification optical system according to the present embodiment, it is desirable that the following conditional expression (8) is satisfied:

$\begin{matrix} {0.500 < {f\; 2{fn}\text{/}f\; 2} < 1.100} & (8) \end{matrix}$ where f2fn denotes a focal length of a most object side lens component in the second lens group, and f2 denotes a focal length of the second lens group.

The conditional expression (8) defines a ratio of the focal length of the most object side lens component in the second lens group relative to the focal length of the second lens group. With satisfying the conditional expression (8), the variable magnification optical system according to the present embodiment can arrange the power of the most object side lens component in the second lens group properly, so that it is possible to correct superbly spherical aberration and other various aberrations.

When the value of f2fn/f2 is equal to or exceeds the upper limit value of the conditional expression (8) of the variable magnification optical system according to the present embodiment, the refractive power of the most object side lens component in the second lens group becomes small, and it becomes difficult to correct superbly spherical aberration and other various aberrations. Meanwhile, in order to secure the advantageous effect of the present embodiment more surely, it is preferable to set the upper limit value of the conditional expression (8) to 1.000. Further, in order to secure the advantageous effect of the present embodiment much more surely, it is preferable to set the upper limit value of the conditional expression (8) to 0.900, and more preferable to 0.850.

On the other hand, when the value of f2fn/f2 in the conditional expression (8) of the variable magnification optical system according to the present embodiment, is equal to or falls below the lower limit value, the refractive power of the most object side lens component in the second lens group becomes large, and it becomes difficult to correct superbly spherical aberration and other various aberrations. Meanwhile, in order to secure the advantageous effect of the variable magnification optical system according to the present embodiment more surely, it is preferable to set the lower limit value of the conditional expression (8) to 0.550. And in order to secure the advantageous effect of the present embodiment much more surely, it is preferable to set the lower limit value of the conditional expression (8) to 0.600 and more preferable to 0.650.

Further, in the variable magnification optical system according to the present embodiment, it is desirable that the following conditional expression (9) is satisfied:

$\begin{matrix} {0.300 < {{{fF}}\text{/}{ft}} < 1.000} & (9) \end{matrix}$ where fF denotes a focal length of the focusing lens group, and ft denotes a focal length of the variable magnification optical system in the telephoto end state.

The conditional expression (9) defines a ratio of the focal length of the focusing lens group relative to the focal length of the variable magnification optical system in the tele photo end state. With satisfying the conditional expression (9), the variable magnification optical system according to the present embodiment can suppress variations in spherical aberration and in other various aberrations upon conducting focusing from an infinite distance object to a close distance object, so that the variable magnification optical system and the lens barrel may be made small in size.

When the value of |fF|/ft is equal to or exceeds the upper limit value of the conditional expression (9) of the variable magnification optical system according to the present embodiment, the refractive power of the focusing lens group becomes small, and it becomes difficult to correct superbly variations in various aberrations and, in particular, variation in spherical aberration upon conducting focusing from an infinite distance object to a close distance object. Meanwhile, in order to secure the advantageous effect of the present embodiment more surely, it is preferable to set the upper limit value of the conditional expression (9) to 0.900. Further, in order to secure the advantageous effect of the present embodiment much more surely, it is preferable to set the upper limit value of the conditional expression (9) to 0.800, and more preferable to 0.750.

On the other hand, when the value of |fF|/ft in the conditional expression (9) of the variable magnification optical system according to the present embodiment, is equal to or falls below the lower limit value, the refractive power of the focusing lens group becomes large, and it becomes difficult to correct superbly variations in various aberrations upon conducting focusing from an infinite distance object to a close distance object and, in particular, variation in spherical aberration. Meanwhile, in order to secure the advantageous effect of the present embodiment more surely, it is preferable to set the lower limit value of the conditional expression (9) to 0.400. And in order to secure the advantageous effect of the present embodiment much more surely, it is preferable to set the lower limit value of the conditional expression (9) to 0.500, and more preferable to 0.550.

In the variable magnification optical system according to the present embodiment, it is desirable that the following conditional expression (10) is satisfied:

$\begin{matrix} {{40.00{^\circ}} < {\omega\; w} < {85.00{^\circ}}} & (10) \end{matrix}$ where ωw denotes a half angle of view of the variable magnification optical system in the wide angle end state.

The conditional expression (10) defines the half angle of view of the variable magnification optical system in the wide angle end state. With satisfying the conditional expression (10), the variable magnification optical system according to the present embodiment can correct superbly various aberrations such as coma aberration, distortion, curvature of field and the like, while maintaining large angle of view.

When the value of ωw is equal to or exceeds the upper limit value of the conditional expression (10) of the variable magnification optical system according to the present embodiment, the angle of view becomes too large and it becomes difficult to correct superbly various aberrations, such as coma aberration, distortion, curvature of field and the like. Meanwhile, in order to secure the advantageous effect of the present embodiment more surely, it is preferable to set the upper limit value of the conditional expression (10) to 84.00°. Further, in order to secure the advantageous effect of the present embodiment much more surely, it is preferable to set the upper limit value of the conditional expression (10) to 83.00°, and more preferable to 82.00°.

On the other hand, when the value of ow in the conditional expression (10) of the variable magnification optical system according to the present embodiment, is equal to or falls below the lower limit value, the angle of view becomes small and it becomes difficult to correct superbly various aberrations. Meanwhile, in order to secure the advantageous effect of the present embodiment more surely, it is preferable to set the lower limit value of the conditional expression (10) to 41.00°. Further, in order to secure the advantageous effect of the present embodiment much more surely, it is preferable to set the lower limit value of the conditional expression (10) to 42.00°, and more preferable to 43.00°.

Further, in the variable magnification optical system according to the present embodiment, it is desirable that the rear lens group comprises a fourth lens group having negative refractive power and a fifth lens group having positive refractive power and that the fourth lens group has a focusing lens group. With this configuration, in the variable magnification optical system according to the present embodiment, the focusing lens group may be made small in size and light in weight, and as a result the variable magnification optical system and the lens barrel may be made small-sized.

The optical apparatus of the present embodiment is equipped with the variable magnification optical system having the above described configuration, so it is possible to realize an optical apparatus which is compatible with a large-sized imaging device in spite that the optical apparatus is small in size, and which can correct superbly various aberrations upon varying magnification as well as upon focusing.

A method for manufacturing a variable magnification optical system according to the present embodiment, is a method for manufacturing a variable magnification optical system which comprises, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a rear lens group having negative refractive power; comprising the steps of:

constructing such that, upon varying a magnification from a wide angle end state to a tele photo end state, a distance between said first lens group and said second lens group is varied, a distance between said second lens group and said third lens group is varied, and a distance between said third lens group and said rear lens group is varied;

constructing such that said third lens group or said rear lens group comprises a focusing lens group which is moved upon carrying out focusing from an infinite distance object to a close distance object; and

constructing such that the following conditional expressions (1) and (2) are satisfied:

$\begin{matrix} {2.00 < {f\; 1\text{/}{fw}} < 8.000} & (1) \\ {0.400 < {{BFw}\text{/}{fw}} < 1.300} & (2) \end{matrix}$

where f1 denotes a focal length of said first lens group, fw denotes a focal length of said variable optical system in a wide angle end state, BFw denotes a back focus of said variable magnification optical system in the wide angle end state, and fw denotes the focal length of said variable magnification optical system in the wide angle end state.

By this method, it is possible to manufacture a variable magnification optical system which is compatible with a large-sized imaging device in spite that the optical system is small-sized, and which can correct superbly various aberrations upon varying magnification as well as upon focusing.

Hereinafter, the variable magnification optical systems relating to numerical examples of the present embodiment will be explained with reference to the accompanying drawings.

First Example

FIG. 1A, FIG. 1B and FIG. 1C are, respectively, cross sectional views in a wide angle end state, in an intermediate focal length state and in a telephoto end state, of a variable magnification optical system according to a First Example of the present embodiment. Arrows below respective lens groups in FIG. 1A show directions of movements of respective lens groups upon varying magnification from the wide angle end state to the intermediate focal length state. Arrows below respective lens groups in FIG. 1B show movement trajectories of respective lens groups upon varying magnification from the intermediate focal length state to the telephoto end state.

The variable magnification optical system according to the present Example is composed of, in order from an object side along the optical axis, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, an aperture stop S, a third lens group G3 having positive refractive power, and a rear lens group GR having negative refractive power.

The first lens group G1 consists of a cemented lens constructed by, in order from the object side along the optical axis, a negative meniscus lens L11 having a convex surface facing the object side cemented with a positive meniscus lens L12 having a convex surface facing the object side.

The second lens group G2 consists of, in order from the object side along the optical axis, a negative meniscus lens L21 having a convex surface facing the object side, a double concave negative lens L22, and a double convex positive lens L23. The negative meniscus lens L21 is a glass mold type aspherical lens whose object side lens surface and image plane I side lens surface are aspherical.

The third lens group G3 consists of, in order from the object side along the optical axis, a double convex positive lens L31, a cemented lens constructed by a positive meniscus lens L32 having a concave surface facing the object side cemented with a negative meniscus lens L33 having a concave surface facing the object side, and a cemented lens constructed by a negative meniscus lens L34 having a convex surface facing the object side cemented with a double convex positive lens L35. The double convex positive lens L31 is a glass mold type aspherical lens whose object side lens surface is aspherical.

The rear lens group GR is composed of, in order from the object side along the optical axis, a fourth lens group G4 having negative refractive power, a fifth lens group G5 having positive refractive power and a sixth lens group G6 having negative refractive power.

The fourth lens group G4 consists of a negative meniscus lens L41 having a convex surface facing the object side. The negative meniscus lens L41 is a glass mold type aspherical lens whose image plane I side lens surface is aspherical.

The fifth lens group G5 consists of a double convex positive lens L51. The double convex positive lens 51 is a glass mold type aspherical lens whose image plane I side lens surface is aspherical.

The sixth lens group G6 consists of, in order from the object side along the optical axis, a positive meniscus lens L61 having a concave surface facing the object side, and a double concave negative lens L62.

A filter FL such as a low pass filter is disposed between the sixth lens group G6 and the image plane I.

On the image plane I, an imaging device (not shown) composed of CCD, CMOS or the like is disposed.

In the variable magnification optical system according to the present Example, upon varying magnification from the wide angle end state to the telephoto end state, all lens groups of the first lens group G1 to the sixth lens group G6 are moved along the optical axis such that a distance between the first lens group G1 and the second lens group G2, a distance between the second lens group G2 and the third lens group G3, a distance between the third lens group G3 and the fourth lens group G4, a distance between the fourth lens group G4 and the fifth lens group G5 and a distance between the fifth lens group G5 and the sixth lens group G6, are varied. The aperture stop S is moved in a body with the third lens group G3 upon varying magnification from the wide angle end state to the telephoto end state.

In the variable magnification optical system according to the present Example, focusing from an infinite distance object to a close distance object is carried out by moving the fourth lens group G4 toward the image plane I along the optical axis as a focusing lens group.

Table 1 below shows various values of the variable magnification optical system relating to the present Example.

In [Surface Data], “m” denotes an order of an optical surface counted from the object side, “r” denotes a radius of curvature, “d” denotes a surface-to-surface distance, that is, an interval from an n-th surface to an (n+1)-th surface, where n is an integer, “nd” denotes refractive index for d-line (wavelength λ=587.6 nm) and “νd” denotes an Abbe number for d-line (wavelength λ=587.6 nm). Further, “OP” denotes an object surface, “Dn” denotes a variable surface-to-surface distance, where n is an integer, “S” denotes an aperture stop, and “I” denotes an image plane. Meanwhile, radius of curvature r=∞ denotes a plane surface, and refractive index of the air nd=1.00000 is omitted. In addition, an aspherical surface is expressed by attaching “*” to the surface number, and in the column of the radius of curvature “r”, a paraxial radius of curvature is shown.

In [Various Data], “f” denotes a focal length, “FNo” denotes an F-number, “ω” denotes a half angle of view (unit “°”), “Y” denotes a maximum image height, and “TL” denotes a total length of the variable magnification optical system according to the present Example, that is, a distance along the optical axis from the first lens surface to the image plane I. “BF” denotes a back focus, that is, a distance on the optical axis from a most image side lens surface to the image plane I, and “BF” (air converted length) is a value of the distance on the optical axis from the most image side lens surface to the image plane I measured in a state where optical block(s) such as filter(s) is(are) removed from on the optical path. Meanwhile, “W” denotes a wide angle end state, “M” denotes an intermediate focal length state, and “T” denotes a tele photo end state.

In [Lens Group Data], a starting surface number “ST” and a focal length “f” of each lens group are shown.

In [Aspherical Surface Data], with respect to aspherical surface(s) shown in [Surface Data], a shape of the aspherical surface is exhibited by the following expression:

X = (h²/r)/[1 + [1 − k(h/r)²]^(1/2)] + A 4h⁴ + A 6h⁶ + A 8h⁸ + A 10y¹⁰

where h denotes a vertical height from the optical axis; X denotes a sag amount which is a distance along the optical axis from the tangent plane at the vertex of the aspherical surface to the aspherical surface at the vertical height h; κ denotes a conical coefficient; A4, A6, A8 and A10 each denotes an aspherical surface coefficient; r denotes a radius of curvature of a reference sphere, that is, a paraxial radius of curvature. Meanwhile, “E−n” denotes “×10^(−n)”, in which “n” is an integer, and for example “1.234E−05” denotes “1.234×10⁻⁵”. The second order aspherical coefficient A2 is 0 and omitted.

In [Variable Distance Data], Dn denotes a surface to surface distance from n-th surface to (n+1)-th surface, where n is an integer. Further, W denotes a wide-angle end state, M denotes an intermediate focal length state, T denotes a telephoto end state, “Infinite” denotes time on which an infinite distance object is focused, and “Close” denotes time on which a close distance object is focused.

In [Values for Conditional Expressions], values with respect to respective conditional expressions are shown.

The focal length f, the radius of curvature r and other units on the length described in Table 1 involve using generally [mm], however, the optical system acquires the equal optical performance even when proportionally enlarged or reduced and is not therefore limited to this unit.

Note that the descriptions of the reference numerals and symbols in Table 1 are the same in the subsequent Examples.

TABLE 1 First Example [Surface Data] m r d nd νd OP ∞  1 55.56269 2.090 1.84666 23.8  2 40.07848 8.659 1.75500 52.3  3 165.87769 D3  *4 305.23816 2.000 1.83357 41.5 *5 15.91291 8.769  6 −46.53317 1.500 1.49782 82.6  7 47.28615 0.150  8 36.78652 3.869 2.00060 25.5  9 −4410.95550 D9  10 (S) ∞ 1.500 *11  25.50000 5.056 1.61881 63.9 12 −55.83871 1.974 13 −29.70567 2.979 1.75500 52.3 14 −17.48858 1.500 1.91435 31.0 15 −26.37061 0.150 16 30.89509 1.500 1.95375 32.3 17 13.37829 4.608 1.59848 57.2 18 −117.59347 D18 19 297.46406 1.500 1.55332 71.7 *20  20.53630 D20 21 143.35194 6.018 1.55332 71.7 *22  −24.59285 D22 23 −42.73323 4.479 1.84666 23.8 24 −25.30641 0.331 25 −31.61248 1.500 1.85026 32.4 26 200.00000 D26 27 ∞ 1.500 1.51680 64.1 28 ∞ D28 I ∞ [Various Data] Variable magnification ratio: 2.75 W M T f 24.72 46.30 67.90 FNo 4.00 4.25 4.00 ω 43.4 24.3 17.0 Y 21.70 21.70 21.70 TL 116.068 129.674 144.273 BF 15.310 32.587 40.396 BF(air converted length) 14.799 32.076 39.885 [Lens Group Data] Lens Group ST f 1^(st) Lens Group 1 113.52 2^(nd) Lens Group 4 −25.53 3^(rd) Lens Group 10 23.75 4^(th) Lens Group 19 −39.94 5^(th) Lens Group 21 38.43 6^(th) Lens Group 23 −57.87 [Aspherical Surface Data] Surface Number: 4 K = 1.00000e+00 A4 = 6.25659e−06 A6 = −1.91556e−08 A8 = 2.52781e−11 A10 = −1.35238e−14 Surface Number: 5 K = 0.00000e+00 A4 = 2.80706e−05 A6 = 6.07832e−08 A8 = −2.35463e−11 A10 = 1.70671e−13 Surface Number: 11 K = 1.00000e+00 A4 = −1.67018e−05 A6 = −1.56513e−09 A8 = 3.10565e−12 A10 = −5.19087e−13 Surface Number: 20 K = 1.00000e+00 A4 = 4.64472e−06 A6 = −7.82369e−08 A8 = 6.72266e−10 A10 = −6.64718e−12 Surface Number: 22 K = 1.00000e+00 A4 = 1.52142e−05 A6 = −5.80147e−09 A8 = −8.01313e−12 A10 = 3.24010e−14 [Variable Distance Data] W M T W M T Infinite Infinite Infinite Close Close Close D3 2.000 16.335 29.807 2.000 16.335 29.807 D9 21.355 7.927 2.222 21.355 7.927 2.222 D18 1.630 1.662 1.111 3.282 5.509 8.035 D20 9.084 9.053 9.604 7.433 5.205 2.680 D22 6.556 1.978 1.000 6.556 1.978 1.000 D26 13.711 30.988 38.797 13.711 30.988 38.797 D28 0.100 0.099 0.099 0.100 0.099 0.099 [Values for Conditional Expressions] (1) f1/fw = 4.5920 (2) BFw/fw = 0.6772 (3) 1/βRw = 0.7639 (4) f1/f1Rw = 5.4336 (5) nd3fp = 1.6188 (6) νd3p = 63.8544 (7) βFw = 2.4956 (8) f2fn/f2 = 0.7915 (9) |fF|/ft = 0.5882 (10)  ωw = 43.4511°

FIG. 2A, FIG. 2B and FIG. 2C are graphs showing various aberrations upon focusing on an infinite distance object, respectively, in the wide angle end state, in the intermediate focal length state and in the telephoto end state, of the variable magnification optical system according to the First Example.

FIG. 3A, FIG. 3B and FIG. 3C are graphs showing various aberrations upon focusing on a close distance object, respectively, in the wide angle end state, in the intermediate focal length state and in the telephoto end state, of the variable magnification optical system according to the First Example.

In the respective graphs showing aberrations, “FNO” denotes an F-number, “NA” denotes a numerical aperture, and “A” denotes an incident angle of light rays, that is, a half angle of view (unit “°”), and “HO” denotes an object height (unit: mm). In detail, in graphs showing spherical aberrations, the value of F-number FNO or numerical aperture NA corresponding to the maximum aperture is shown. In graphs showing astigmatism and distortions, the maximum values of the half angle of view or the maximum object height are shown respectively, and in graphs showing coma aberration, each half angle of view or each object height is shown. “d” denotes aberration for d-line (wavelength λ=587.6 nm), “g” denotes aberration for g-line (wavelength λ=435.8 nm), and graphs with “g” or “d” being not attached, show aberration for d-line. In graphs showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. In graphs showing coma aberration, coma aberration in each half angle of view or each object height, that is, transverse aberration is shown. Meanwhile, in graphs showing various aberrations in the respective Examples as described below, the same symbols as in the present Example are employed.

As is apparent from the above-mentioned graphs showing aberrations, the variable magnification optical system relating to the present Example can correct superbly various aberrations over the wide angle end state to the telephoto end state and has excellent imaging performance, and further has excellent imaging performance even upon focusing on a close distance object.

Second Example

FIG. 4A, FIG. 4B and FIG. 4C are, respectively, cross sectional views in a wide angle end state, in an intermediate focal length state and in a telephoto end state, of a variable magnification optical system according to a Second Example of the variable magnification optical system of the present embodiment. Arrows below respective lens groups in FIG. 4A show directions of movements of respective lens groups upon varying magnification from the wide angle end state to the intermediate focal length state. Arrows below respective lens groups in FIG. 4B show movement trajectories of respective lens groups upon varying magnification from the intermediate focal length state to the telephoto end state.

The variable magnification optical system according to the present Example is composed of, in order from the object side along the optical axis, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, an aperture stop S, a third lens group G3 having positive refractive power, and a rear lens group GR having negative refractive power.

The first lens group G1 consists of a cemented lens constructed by, in order from the object side along the optical axis, a negative meniscus lens L11 having a convex surface facing the object side cemented with a positive meniscus lens L12 having a convex surface facing the object side.

The second lens group G2 consists of, in order from the object side along the optical axis, a negative meniscus lens L21 having a convex surface facing the object side, a double concave negative lens L22, and a positive meniscus lens L23 having a convex surface facing the object side. The negative meniscus lens L21 is a glass mold type aspherical lens whose object side lens surface and image plane I side lens surface are aspherical.

The third lens group G3 consists of, in order from the object side along the optical axis, a positive meniscus lens L31 having a convex surface facing the object side, a positive meniscus lens L32 having a convex surface facing the object side, a cemented lens constructed by a positive meniscus lens L33 having a convex surface facing the object side cemented with a negative meniscus lens L34 having a convex surface facing the object side, and a double convex positive lens L35. The positive meniscus lens L31 is a glass mold type aspherical lens whose object side lens surface is aspherical. The double convex positive lens L35 is a glass mold type aspherical lens whose object side lens surface and image plane I side lens surface are aspherical.

The rear lens group GR is composed of, in order from the object side along the optical axis, a fourth lens group G4 having negative refractive power and a fifth lens group G5 having positive refractive power.

The fourth lens group G4 consists of a negative meniscus lens L41 having a convex surface facing the object side. The negative meniscus lens L41 is a glass mold type aspherical lens whose object side lens surface is aspherical.

The fifth lens group G5 consists of a positive meniscus lens group L51 having a concave surface facing the object side.

A filter FL such as a low pass filter is disposed between the fifth lens group G5 and the image plane I.

On the image plane I, an imaging device (not shown) composed of CCD, CMOS or the like is disposed.

In the variable magnification optical system according to the present Example, upon varying magnification from the wide angle end state to the telephoto end state, the first lens group G1, the second lens group G2, the third lens group G3 and the fourth lens group G4 are moved along the optical axis such that a distance between the first lens group G1 and the second lens group G2, a distance between the second lens group G2 and the third lens group G3, a distance between the third lens group G3 and the fourth lens group G4, and a distance between the fourth lens group G4 and the fifth lens group G5, are varied. At this time, the fifth lens group G5 is fixed relative to the image plane I. The aperture stop S is moved in a body with the third lens group G3 upon varying magnification from the wide angle end state to the telephoto end state.

In the variable magnification optical system according to the present Example, focusing from an infinite distance object to a close distance object is carried out by moving the positive lens L35 of the third lens group G3 toward the object along the optical axis as a focusing lens group.

Table 2 below shows various values of the variable magnification optical system relating to the present Example.

TABLE 2 Second Example [Surface Data] m r d nd νd OP ∞  1 80.37239 2.191 1.84666 23.8  2 51.98777 8.571 1.75500 52.3  3 2070.67650 D3  *4 641.99827 2.000 1.85135 40.1 *5 16.81311 8.912  6 −42.25332 1.500 1.49782 82.6  7 110.99976 0.132  8 41.80583 3.451 2.00069 25.5  9 1058.33950 D9  10 (S) ∞ 1.500 *11  39.00831 2.770 1.49710 81.5 12 140.27569 0.100 13 43.60704 3.000 1.85896 22.7 14 289.56516 0.100 15 18.65400 3.904 1.49782 82.6 16 75.27582 1.500 1.85896 22.7 17 16.91540 7.449 *18  23.17679 5.123 1.49710 81.5 *19  −24.33043 D19 *20  99.02941 1.500 1.74330 49.3 21 22.73753 D21 22 −272.28910 4.264 1.48749 70.3 23 −65.54087 16.319  24 ∞ 1.500 1.51680 64.1 25 ∞ D25 I ∞ [Various Data] Variable magnification ratio 2.75 W M T f 24.72 46.31 67.90 FNo 4.00 4.00 4.00 ω 43.4 23.6 16.5 Y 21.70 21.70 21.70 TL 115.511 129.313 146.760 BF 17.920 17.921 17.921 BF(air converted length) 17.409 17.410 17.410 [Lens Group Data] Lens Group ST f 1^(st) Lens Group 1 118.36 2^(nd) Lens Group 4 −26.19 3^(rd) Lens Group 10 24.69 4^(th) Lens Group 20 −40.04 5^(th) Lens Group 22 175.88 [Aspherical Surface Data] Surface Number: 4 K = 1.00000e+00 A4 = 4.80528e−06 A6 = −2.54101e−08 A8 = 4.94759e−11 A10 = −4.51789e−14 Surface Number: 5 K = 0.00000e+00 A4 = 2.73459e−05 A6 = 3.32316e−08 A8 = 9.23524e−12 A10 = −2.12635e−13 Surface Number: 11 K = 1.00000e+00 A4 = −5.44666e−06 A6 = −6.91574e−09 A8 = −1.69497e−11 A10 = 3.80992e−13 Surface Number: 18 K = 1.00000e+00 A4 = −2.14682e−05 A6 = 1.69238e−07 A8 = −7.34656e−11 A10 = −4.73585e−12 Surface Number: 19 K = 1.00000e+00 A4 = 2.20572e−05 A6 = 1.07214e−07 A8 = 3.49803e−10 A10 = −7.90497e−12 Surface Number: 20 K = 1.00000e+00 A4 = 4.65831e−07 A6 = 4.17596e−08 A8 = −6.57210e−10 A10 = 0.00000e+00 [Variable Distance Data] W M T W M T Infinite Infinite Infinite Close Close Close D3 2.000 18.199 30.446 2.000 18.199 30.446 D9 22.008 6.706 1.701 22.008 6.706 1.701 D19 3.665 3.116 1.770 4.734 6.005 7.453 D21 11.952 25.405 36.955 11.952 25.405 36.955 D25 0.101 0.102 0.102 0.101 0.102 0.102 [Values for Conditional Expressions] (1) f1/fw = 4.7877 (2) BFw/fw = 0.8942 (3) 1/βRw = 1.1035 (4) f1/f1Rw = 5.5459 (5) nd3fp = 1.4971 (6) νd3p = 81.5584 (7) βFw = −0.0064 (8) f2fn/f2 = 0.7755 (9) |fF|/ft = 0.3645 (10)  ωw = 43.4244°

FIG. 5A, FIG. 5B and FIG. 5C are graphs showing various aberrations upon focusing on an infinite distance object, respectively, in the wide angle end state, in the intermediate focal length state and in the telephoto end state, of the variable magnification optical system according to the Second Example.

FIG. 6A, FIG. 6B and FIG. 6C are graphs showing various aberrations upon focusing on a close distance object, respectively, in the wide angle end state, in the intermediate focal length state and in the telephoto end state, of the variable magnification optical system according to the Second Example.

As is apparent from the above-mentioned graphs showing aberrations, the variable magnification optical system relating to the present Example can correct superbly various aberrations over the wide angle end state to the telephoto end state and has excellent imaging performance, and further has excellent imaging performance even upon focusing on a close distance object.

Third Example

FIG. 7A, FIG. 7B and FIG. 7C are, respectively, cross sectional views in a wide angle end state, in an intermediate focal length state and in a telephoto end state, of a variable magnification optical system according to a Third Example of the variable magnification optical system of the present embodiment. Arrows below respective lens groups in FIG. 7A show directions of movements of respective lens groups upon varying magnification from the wide angle end state to the intermediate focal length state. Arrows below respective lens groups in FIG. 7B show movement trajectories of respective lens groups upon varying magnification from the intermediate focal length state to the telephoto end state.

The variable magnification optical system according to the present Example is composed of, in order from an object side along the optical axis, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, an aperture stop S, a third lens group G3 having positive refractive power, and a rear lens group GR having negative refractive power.

The first lens group G1 consists of a cemented lens constructed by, in order from the object side along the optical axis, a negative meniscus lens L11 having a convex surface facing the object side cemented with a positive meniscus lens L12 having a convex surface facing the object side.

The second lens group G2 consists of, in order from the object side along the optical axis, a negative meniscus lens L21 having a convex surface facing the object side, a double concave negative lens L22, and a positive meniscus lens L23 having a convex surface facing the object side. The negative meniscus lens L21 is a glass mold type aspherical lens whose object side lens surface and image plane I side lens surface are aspherical.

The third lens group G3 consists of, in order from the object side along the optical axis, a positive meniscus lens L31 having a convex surface facing the object side, a double convex positive lens L32, a cemented lens constructed by a double convex positive lens L33 cemented with a double concave negative lens L34, and a double convex positive lens L35. The positive meniscus lens L31 is a glass mold type aspherical lens whose object side lens surface is aspherical. The double convex positive lens L35 is a glass mold type aspherical lens whose object side lens surface and image plane I side lens surface are aspherical.

The rear lens group GR is composed of, in order from the object side along the optical axis, a fourth lens group G4 having negative refractive power and a fifth lens group G5 having negative refractive power.

The fourth lens group G4 consists of a positive meniscus lens L41 having a concave surface facing the object side and a double concave negative lens L42. The double concave negative lens L42 is a glass mold type aspherical lens whose object side lens surface and image plane I side lens surface are aspherical.

The fifth lens group G5 consists of a negative meniscus lens group L51 having a concave surface facing the object side.

A filter FL such as a low pass filter is disposed between the fifth lens group G5 and the image plane I.

On the image plane I, an imaging device (not shown) composed of CCD, CMOS or the like is disposed.

In the variable magnification optical system according to the present Example, upon varying magnification from the wide angle end state to the telephoto end state, the first lens group G1, the second lens group G2, the third lens group G3 and the fourth lens group G4 are moved along the optical axis such that a distance between the first lens group G1 and the second lens group G2, a distance between the second lens group G2 and the third lens group G3, a distance between the third lens group G3 and the fourth lens group G4, and a distance between the fourth lens group G4 and the fifth lens group G5, are varied. At this time, the fifth lens group G5 is fixed relative to the image plane I. The aperture stop S is moved in a body with the third lens group G3 upon varying magnification from the wide angle end state to the telephoto end state.

In the variable magnification optical system according to the present Example, focusing from an infinite distance object to a close distance object is carried out by moving the fourth lens group G4 toward the image plane I along the optical axis as a focusing lens group.

Table 3 below shows various values of the variable magnification optical system relating to the present Example.

TABLE 3 Third Example [Surface Data] m r d nd νd OP ∞  1 89.76586 2.265 1.91255 19.4  2 66.23033 7.686 1.72916 54.6  3 2195.99100 D3  *4 277.38836 2.000 1.88079 37.3 *5 17.49175 8.770  6 −57.48461 1.500 1.49782 82.6  7 51.02263 0.150  8 35.06470 4.055 2.04370 27.2  9 245.04447 D9  10 (S) ∞ 1.500 *11  26.08134 2.954 1.49710 81.5 12 64.38198 0.150 13 42.81458 3.000 1.85896 22.7 14 −408.89472 1.730 15 33.86607 4.307 1.49782 82.6 16 −67.66664 1.500 1.85896 22.7 17 20.59315 3.307 *18  24.88849 5.009 1.49710 81.5 *19  −20.31236 D19 20 −55.34887 2.804 1.92119 24.0 21 −30.11397 1.627 *22  −37.35916 1.500 1.79864 45.4 *23  56.50097 D23 24 −115.79135 1.614 1.48749 70.3 25 −121.94772 13.000  26 ∞ 1.500 1.51680 64.1 27 ∞ D27 I ∞ [Various Data] Variable magnification ratio 2.75 W M T f 24.72 46.31 67.90 FNo 4.00 4.00 4.00 ω 43.5 23.5 16.4 Y 21.70 21.70 21.70 TL 116.411 128.891 146.759 BF 14.601 14.601 14.601 BF(air converted length) 14.089 14.090 14.090 [Lens Group Data] Lens Group ST f 1^(st) Lens Group 1 140.58 2^(nd) Lens Group 4 −27.73 3^(rd) Lens Group 10 25.37 4^(th) Lens Group 20 −47.81 5^(th) Lens Group 24 −5147.18 [Aspherical Surface Data] Surface Number: 4 K = 1.00000e+00 A4 = 8.89487e−06 A6 = −5.32351e−08 A8 = 1.15340e−10 A10 = −9.61968e−14 Surface Number: 5 K = 0.00000e+00 A4 = 3.06664e−05 A6 = 4.19740e−08 A8 = −3.78170e−10 A10 = 1.10549e−12 Surface Number: 11 K = 1.00000e+00 A4 = −1.43493e−05 A6 = −1.64931e−08 A8 = −1.16757e−10 A10 = 5.06940e−13 Surface Number: 18 K = 1.00000e+00 A4 = −5.15936e−06 A6 = −8.80397e−08 A8 = 2.04540e−09 A10 = −5.99297e−12 Surface Number: 19 K = 1.00000e+00 A4 = 3.60122e−05 A6 = −1.84722e−07 A8 = 2.16592e−09 A10 = −2.51269e−12 Surface Number: 22 K = 1.00000e+00 A4 = 3.47799e−05 A6 = −5.63856e−07 A8 = 5.11223e−09 A10 = −2.14413e−11 Surface Number: 23 K = 1.00000e+00 A4 = 4.08762e−05 A6 = −4.22039e−07 A8 = 3.84567e−09 A10 = −1.33757e−11 [Variable Distance Data] W M T W M T Infinite Infinite Infinite Close Close Close D3 2.000 21.368 35.662 2.000 21.368 35.662 D9 25.688 8.326 2.837 25.688 8.326 2.837 D19 3.296 3.360 1.742 5.189 7.744 8.532 D23 13.398 23.808 34.489 11.505 19.424 27.699 D27 0.101 0.101 0.101 0.101 0.101 0.101 [Values for Conditional Expressions] (1) f1/fw = 5.6876 (2) BFw/fw = 0.6726 (3) 1/βRw = 0.9927 (4) f1/f1Rw = 6.3490 (5) nd3fp = 1.4971 (6) νd3p = 81.5584 (7) βFw = 1.5940 (8) f2fn/f2 = 0.7670 (9) |fF|/ft = 0.7042 (10)  ωw = 43.4653°

FIG. 8A, FIG. 8B and FIG. 8C are graphs showing various aberrations upon focusing on an infinite distance object, respectively, in the wide angle end state, in the intermediate focal length state and in the telephoto end state, of the variable magnification optical system according to the Third Example.

FIG. 9A, FIG. 9B and FIG. 9C are graphs showing various aberrations upon focusing on a close distance object, respectively, in the wide angle end state, in the intermediate focal length state and in the telephoto end state, of the variable magnification optical system according to the Third Example.

As is apparent from the above-mentioned graphs showing aberrations, the variable magnification optical system relating to the present Example can correct superbly various aberrations over the wide angle end state to the telephoto end state and has excellent imaging performance, and further has excellent imaging performance even upon focusing on a close distance object.

Fourth Example

FIG. 10A, FIG. 10B and FIG. 10C are, respectively, cross sectional views in a wide angle end state, in an intermediate focal length state and in a telephoto end state, of a variable magnification optical system according to a Fourth Example of the variable magnification optical system of the present embodiment. Arrows below respective lens groups in FIG. 10A show directions of movements of respective lens groups upon varying magnification from the wide angle end state to the intermediate focal length state. Arrows below respective lens groups in FIG. 10B show movement trajectories of respective lens groups upon varying magnification from the intermediate focal length state to the telephoto end state.

The variable magnification optical system according to the present Example is composed of, in order from an object side along the optical axis, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, an aperture stop S, a third lens group G3 having positive refractive power, and a rear lens group GR having negative refractive power.

The first lens group G1 consists of a cemented lens constructed by, in order from the object side along the optical axis, a negative meniscus lens L11 having a convex surface facing the object side cemented with a positive meniscus lens L12 having a convex surface facing the object side.

The second lens group G2 consists of, in order from the object side along the optical axis, a double concave negative lens L21, a double concave negative lens L22, and a double convex positive lens L23. The double concave negative lens L21 is a glass mold type aspherical lens whose object side lens surface and image plane I side lens surface are aspherical.

The third lens group G3 consists of, in order from the object side along the optical axis, a positive meniscus lens L31 having a convex surface facing the object side, a double convex positive lens L32, a cemented lens constructed by a double convex positive lens L33 cemented with a double concave negative lens L34, and a double convex positive lens L35. The positive meniscus lens L31 is a glass mold type aspherical lens whose object side lens surface is aspherical. The double convex positive lens L35 is a glass mold type aspherical lens whose object side lens surface and image plane I side lens surface are aspherical.

The rear lens group GR consists of a fourth lens group G4 having negative refractive power.

The fourth lens group G4 consists of a double convex positive lens L41 and a double concave negative lens L42. The double concave negative lens L42 is a glass mold type aspherical lens whose image plane I side lens surface is aspherical.

A filter FL such as a low pass filter is disposed between the fourth lens group G4 and the image plane I.

On the image plane I, an imaging device (not shown) composed of CCD, CMOS or the like is disposed.

In the variable magnification optical system according to the present Example, upon varying magnification from the wide angle end state to the telephoto end state, all lens groups of the first lens group G1 to the fourth lens group G4 are moved along the optical axis such that a distance between the first lens group Cl and the second lens group G2, a distance between the second lens group G2 and the third lens group G3, and a distance between the third lens group G3 and the fourth lens group G4, are varied. The aperture stop S is moved in a body with the third lens group G3 upon varying magnification from the wide angle end state to the telephoto end state.

In the variable magnification optical system according to the present Example, focusing from an infinite distance object to a close distance object is carried out by moving the fourth lens group G4 along the optical axis toward the image plane I as a focusing lens group.

Table 4 below shows various values of the variable magnification optical system relating to the present Example.

TABLE 4 Fourth Example [Surface Data] m r d nd νd OP ∞  1 87.62477 2.150 1.84666 23.8  2 57.73166 8.600 1.75500 52.3  3 1380.47940 D3  *4 −252.60716 2.000 1.85135 40.1 *5 19.73259 11.312   6 −40.46779 1.500 1.49782 82.6  7 146.36804 0.100  8 64.01884 4.055 2.00100 29.1  9 −126.68848 D9  10 (S) ∞ 1.500 *11  30.22445 3.000 1.59201 67.0 12 51.27630 5.037 13 57.69494 3.000 1.85896 22.7 14 −45.14666 0.100 15 106.93037 4.300 1.49782 82.6 16 −30.19382 1.500 1.85896 22.7 17 23.72608 2.966 *18  23.40247 6.000 1.49710 81.5 *19  −18.45086 D19 20 757.78393 2.800 1.92119 24.0 21 −62.34786 0.172 22 −73.09604 1.500 1.80139 45.5 *23  26.98448 D23 24 ∞ 1.500 1.51680 64.1 25 ∞ D25 I ∞ [Various Data] Variable magnification ratio 2.75 W M T f 24.72 46.32 67.90 FNo 4.00 4.00 4.00 ω 44.8 24.2 16.7 Y 21.70 21.70 21.70 TL 123.661 134.611 154.520 BF 32.085 47.771 58.404 BF(air converted length) 31.574 47.260 57.893 [Lens Group Data] Lens Group ST f 1^(st) Lens Group 1 132.04 2^(nd) Lens Group 4 −30.82 3^(rd) Lens Group 10 25.48 4^(th) Lens Group 20 −41.00 [Aspherical Surface Data] Surface Number: 4 K = 1.00000e+00 A4 = 9.70747e−06 A6 = −3.52770e−08 A8 = 6.58152e−11 A10 = −4.95165e−14 Surface Number: 5 K = 0.00000e+00 A4 = 2.00742e−05 A6 = 3.39646e−08 A8 = −2.35998e−10 A10 = 6.14412e−13 Surface Number: 11 K = 1.00000e+00 A4 = −1.87683e−05 A6 = −3.17314e−08 A8 = −8.74929e−11 A10 = 1.27393e−13 Surface Number: 18 K = 1.00000e+00 A4 = −2.29499e−05 A6 = −5.63341e−08 A8 = 5.89446e−10 A10 = −2.45654e−12 Surface Number: 19 K = 1.00000e+00 A4 = 2.51719e−05 A6 = −1.53372e−07 A8 = 1.18933e−09 A10 = −4.11191e−12 Surface Number: 23 K = 1.00000e+00 A4 = −2.18656e−06 A6 = 7.65289e−08 A8 = −5.83461e−10 A10 = 2.30823e−12 [Variable Distance Data] W M T W M T Infinite Infinite Infinite Close Close Close D3 2.000 18.027 34.324 2.000 18.027 34.324 D9 24.453 5.483 0.100 24.453 5.483 0.100 D19 3.531 1.737 0.100 4.979 4.625 4.590 D23 30.484 46.169 56.802 29.035 43.281 52.312 D25 0.101 0.102 0.102 0.101 0.102 0.103 [Values for Conditional Expressions] (1) f1/fw = 4.8288 (2) BFw/fw = 1.2164 (3) 1/βRw = 0.6139 (4) f1/f1Rw = 5.5629 (5) nd3fp = 1.4971 (6) νd3p = 81.5584 (7) βFw = 1.6289 (8) f2fn/f2 = 0.7305 (9) |fF|/ft = 0.6426 (10)  ωw = 44.2631°

FIG. 11A, FIG. 11B and FIG. 11C are graphs showing various aberrations upon focusing on an infinite distance object, respectively, in the wide angle end state, in the intermediate focal length state and in the telephoto end state, of the variable magnification optical system according to the Fourth Example.

FIG. 12A, FIG. 12B and FIG. 12C are graphs showing various aberrations upon focusing on a close distance object, respectively, in the wide angle end state, in the intermediate focal length state and in the telephoto end state, of the variable magnification optical system according to the Fourth Example.

As is apparent from the above-mentioned graphs showing aberrations, the variable magnification optical system relating to the present Example can correct superbly various aberrations over the wide angle end state to the telephoto end state and has excellent imaging performance, and further has excellent imaging performance even upon focusing on a close distance object.

Fifth Example

FIG. 13A, FIG. 13B and FIG. 13C are, respectively, cross sectional views in a wide angle end state, in an intermediate focal length state and in a telephoto end state, of a variable magnification optical system according to a Fifth Example of the variable magnification optical system of the present embodiment. Arrows below respective lens groups in FIG. 13A show directions of movements of respective lens groups upon varying magnification from the wide angle end state to the intermediate focal length state. Arrows below respective lens groups in FIG. 13B show movement trajectories of respective lens groups upon varying magnification from the intermediate focal length state to the telephoto end state.

The variable magnification optical system according to the present Example is composed of, in order from the object side along the optical axis, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, an aperture stop S, a third lens group G3 having positive refractive power, and a rear lens group GR having negative refractive power.

The first lens group G1 consists of a cemented lens constructed by, in order from the object side along the optical axis, a negative meniscus lens L11 having a convex surface facing the object side cemented with a double convex positive lens L12.

The second lens group G2 consists of, in order from the object side along the optical axis, a double concave negative lens L21, a double concave negative lens L22, and a positive meniscus lens L23 having a convex surface facing the object side. The double concave negative lens L21 is a glass mold type aspherical lens whose image plane I side lens surface is aspherical.

The third lens group G3 consists of, in order from the object side along the optical axis, a double convex positive lens L31, a double convex positive lens L32, a cemented lens constructed by a double convex positive lens L33 cemented with a double concave negative lens L34, and a double convex positive lens L35. The double convex positive lens L31 is a glass mold type aspherical lens whose object side lens surface is aspherical. The double convex positive lens L35 is a glass mold type aspherical lens whose object side lens surface is aspherical.

The rear lens group GR is composed of a fourth lens group G4 having negative refractive power.

The fourth lens group G4 consists of a double convex positive lens L41 and a double concave negative lens L42. The double concave negative lens L42 is a glass mold type aspherical lens whose object side lens surface is aspherical.

A filter FL such as a low pass filter is disposed between the fourth lens group G4 and the image plane I.

On the image plane I, an imaging device (not shown) composed of CCD, CMOS or the like is disposed.

In the variable magnification optical system according to the present Example, upon varying magnification from the wide angle end state to the telephoto end state, all lens groups of the first lens group G1 to the fourth lens group G4 are moved along the optical axis such that a distance between the first lens group G1 and the second lens group G2, a distance between the second lens group G2 and the third lens group G3, and a distance between the third lens group G3 and the fourth lens group G4, are varied. The aperture stop S is moved in a body with the third lens group G3 upon varying magnification from the wide angle end state to the telephoto end state.

In the variable magnification optical system according to the present Example, focusing from an infinite distance object to a close distance object is carried out by moving the fourth lens group G4 toward the image plane I along the optical axis as a focusing lens group.

Table 5 below shows various values of the variable magnification optical system relating to the present Example.

TABLE 5 Fifth Example [Surface Data] m r d nd νd OP ∞  1 119.32600 2.150 1.84666 23.8  2 68.71728 8.600 1.75500 52.3  3 −1041.56390 D3   4 −457.17100 2.000 1.85135 40.1 *5 20.61283 7.414  6 −71.55363 1.500 1.49782 82.6  7 108.27671 0.100  8 42.73022 4.055 2.00069 25.5  9 567.23839 D9  10 (S) ∞ 1.500 *11  49.74902 2.954 1.55332 71.7 12 −831.68070 5.492 13 119.77899 3.000 1.86074 23.1 14 −32.91562 0.100 15 788.35305 4.307 1.49782 82.6 16 −22.05418 1.500 1.86074 23.1 17 30.00000 3.522 *18  41.01853 7.000 1.59201 67.0 19 −22.23377 D19 20 1063.64530 2.804 1.90200 25.3 21 −64.43734 3.021 *22  −73.11499 1.500 1.80139 45.5 23 30.53440 D23 24 ∞ 1.500 1.51680 64.1 25 ∞ D25 I ∞ [Various Data] Variable magnification ratio 2.75 W M T f 24.72 46.31 67.90 FNo 4.00 4.00 4.00 ω 43.3 22.1 15.4 Y 20.00 20.00 20.00 TL 116.346 132.760 149.927 BF 20.082 35.787 48.197 BF(air converted length) 19.571 35.276 47.686 [Lens Group Data] Lens Group ST f 1^(st) Lens Group 1 154.54 2^(nd) Lens Group 4 −34.53 3^(rd) Lens Group 10 28.38 4^(th) Lens Group 20 −48.62 [Aspherical Surface Data] Surface Number: 5 K = 0.00000e+00 A4 = 1.27904e−05 A6 = 4.25474e−08 A8 = −1.06207e−10 A10 = 3.28727e−13 Surface Number: 11 K = 1.00000e+00 A4 = −2.37429e−05 A6 = −4.66597e−09 A8 = −4.37585e−10 A10 = 2.03678e−12 Surface Number: 18 K = 1.00000e+00 A4 = −1.38634e−05 A6 = 3.10542e−08 A8 = −4.01477e−11 A10 = 9.01450e−14 Surface Number: 22 K = 1.00000e+00 A4 = −4.04480e−06 A6 = −1.42432e−08 A8 = 1.81173e−10 A10 = −7.62702e−13 [Variable Distance Data] W M T W M T Infinite Infinite Infinite Close Close Close D3 2.000 23.094 37.212 2.000 23.094 37.212 D9 23.685 7.628 1.000 23.685 7.628 1.000 D19 8.059 3.733 1.000 9.929 6.663 5.153 D23 18.482 34.186 46.595 16.612 31.256 42.442 D25 0.101 0.101 0.102 0.101 0.101 0.102 [Values for Conditional Expressions] (1) f1/fw = 6.2515 (2) BFw/fw = 0.8702 (3) 1/βRw = 0.7392 (4) f1/f1Rw = 6.8464 (5) nd3fp = 1.5533 (6) νd3p = 71.6835 (7) βFw = 1.3529 (8) f2fn/f2 = 0.6696 (9) |fF|/ft = 0.7160 (10)  ωw = 46.7678°

FIG. 14A, FIG. 14B and FIG. 14C are graphs showing various aberrations upon focusing on an infinite distance object, respectively, in the wide angle end state, in the intermediate focal length state and in the telephoto end state, of the variable magnification optical system according to the Fifth Example.

FIG. 15A, FIG. 15B and FIG. 15C are graphs showing various aberrations upon focusing on a close distance object, respectively, in the wide angle end state, in the intermediate focal length state and in the telephoto end state, of the variable magnification optical system according to the Fifth Example.

As is apparent from the above-mentioned graphs showing aberrations, the variable magnification optical system relating to the present Example can correct superbly various aberrations over the wide angle end state to the telephoto end state and has excellent imaging performance, and further has excellent imaging performance even upon focusing on a close distance object.

According to the above described respective examples, it is possible to realize a variable magnification optical system which is compatible with a large-sized imaging device in spite that the optical system is small-sized, and which can correct superbly various aberrations upon varying magnification over the wide angle end state to the telephoto end state, and further has excellent imaging performance even upon focusing on a close distance object.

Meanwhile, in the variable magnification optical system relating to the present embodiment, a variable magnification ratio is on the order of 2 times to 10 times and a 35 mm-size converted focal length in the wide angle end state is on the order of 20 to 30 mm. Further, in the variable magnification optical system relating to the present embodiment, an F-number in the wide angle end state is on the order of f/2.0 to f/4.5, and the F-number in the tele photo end state is on the order of f/2.0 to f/6.3.

Further, each of the above described Examples is a concrete example of the present embodiment, and the present embodiment is not limited to the above described Examples. The contents described below can be adopted without deteriorating optical performance of the variable magnification optical systems according to the present embodiment.

Although variable magnification optical systems having a four group configuration, a five group configuration or a six group configuration were illustrated above as numerical examples of the variable magnification optical systems according to the present embodiment, the present embodiment is not limited to them and variable magnification optical systems having other configurations, such as seven group configuration, or the like, can be configured. Concretely, a configuration that a lens or a lens group is added to the most object side or to the most image side of the variable magnification optical system according to each of the above described Examples is possible. Alternatively, a lens or a lens group may be added between the first lens group G1 and the second lens group G2. Alternatively, a lens or a lens group may be added between the second lens group G2 and the third lens group G3. Alternatively, a lens or a lens group may be added between the third lens group G3 and the rear lens group GR.

Further, in each of the above described Examples, configurations that the rear lens group GR is composed of the fourth lens group G4, or of the fourth lens group G4 and the fifth lens group G5, or of the fourth lens group G4, the fifth lens group G5 and the sixth lens groups G6, were illustrated, but configurations are not limited to them.

Further, in each of the above described Examples, the focusing lens group is composed of one lens group or of a part of one lens group, but the focusing lens group may be composed of two or more lens groups. Auto focusing can be applied for such focusing group(s), and drive by motor for auto focusing, such as, ultrasonic motor, stepping motor VCM motor may be suitably adopted.

Further, in the variable magnification optical systems according to each of the above described Examples, any lens group in the entirety thereof or a portion thereof can be moved in a direction including a component perpendicular to the optical axis as a vibration reduction lens group, or rotationally moved (swayed) in an in-plane direction including the optical axis, whereby a configuration of a vibration reduction can be taken.

Further, in the variable magnification optical systems according to each of the above described Examples, a lens surface of a lens may be a spherical surface, a plane surface, or an aspherical surface. When a lens surface is a spherical surface or a plane surface, lens processing, assembling and adjustment become easy, and it is possible to prevent deterioration in optical performance caused by lens processing, assembling and adjustment errors, so that it is preferable. Moreover, even if an image plane is shifted, deterioration in depiction performance is little, so that it is preferable. When a lens surface is an aspherical surface, the aspherical surface may be fabricated by a grinding process, a glass molding process that a glass material is formed into an aspherical shape by a mold, or a compound type process that a resin material is formed into an aspherical shape on a glass lens surface. A lens surface may be a diffractive optical surface, and a lens may be a graded-index type lens (GRIN lens) or a plastic lens.

Further, in the variable magnification optical systems according to each of the above described Examples, it is preferable that the aperture stop S is disposed between the second lens group G2 and the third lens group G3, but the function may be substituted by a lens frame without disposing a member as an aperture stop.

Further, the lens surface(s) of the lenses configuring the variable magnification optical systems according to each of the above described Examples, may be coated with anti-reflection coating(s) having a high transmittance in a wide wavelength region. With this contrivance, it is feasible to reduce a flare as well as ghost and attain excellent optical performance with high contrast.

Next, a camera equipped with the variable magnification optical system according to the present embodiment, will be explained with referring to FIG. 16 .

FIG. 16 is a view showing a configuration of the camera equipped with the variable magnification optical system according to the present embodiment.

The camera 1 as shown in FIG. 16 , is a so-called mirror-less camera of a lens interchangeable type equipped with the variable magnification optical system according to the first Example as an imaging lens 2.

In the present camera 1, a light emitted from an unillustrated object (an object to be photo-taken) is converged by the imaging lens 2, through an unillustrated OLPF (Optical low pass filter), and forms an image of the object on an imaging plane of an image pick-up portion 3. The light from the object is photo-electrically converted through a photo-electric conversion element provided on the image pick-up portion 3 to form a picture image of the object. This picture image is displayed on an EVF (electric view finder) 4 provided on the camera 1. Accordingly, a photographer can observe the object to be photo-taken through the EVF 4.

Further, upon unillustrated release button being depressed by the photographer, the picture image of the object formed by the image pick-up portion 3 is stored in an unillustrated memory. Thus, the photographer can take a photo of the object.

It is noted here that the variable magnification optical system relating to the First Example in which the present camera 1 is equipped with the imaging lens 2, has superb optical performance as described above and is made small in size. In other words, the present camera 1 can be made small in size and attain superb optical performances that various aberrations can be corrected well from the wide angle end state to the telephoto end state and excellent imaging performance is attained even upon focusing on a close distance object.

Incidentally, when there is configured a camera in which the variable magnification optical system according to any of the before-mentioned Second to Fifth Examples is installed as the imaging lens 2, the camera also can attain the same effects as those of the above-mentioned camera 1. Further, even when the variable magnification optical system according to any of the above Examples is installed in a camera of a single lens reflex type equipped with a quick return mirror in which the object image is observed through a finder optical system, the camera also can attain the same effects as those of the above-mentioned camera 1.

Next, an outline of a method for manufacturing the variable magnification optical system according to the present embodiment, is described with referring to FIG. 17 .

FIG. 17 is a flowchart schematically showing a method for manufacturing the variable magnification optical system according to the present embodiment.

The method for manufacturing the variable magnification optical system according to the present embodiment shown in FIG. 17 , is a method for manufacturing a variable magnification optical system which comprises, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power and a rear lens group having negative refractive power; the method comprising the following steps S1 to S3.

Step S1: constructing such that, upon varying a magnification from a wide angle end state to a telephoto end state, a distance between the first lens group and the second lens group is varied, a distance between the second lens group and the third lens group is varied, and a distance between the third lens group and the rear lens group is varied.

Step S2: constructing such that the third lens group or the rear lens group comprises a focusing lens group which is moved upon carrying out focusing from an infinite distance object to a close distance object.

Step S3: constructing such that the variable magnification optical system satisfies the following conditional expressions (1) and (2):

$\begin{matrix} {2.00 < {f\; 1\text{/}{fw}} < 8.000} & (1) \\ {0.400 < {{BFw}\text{/}{fw}} < 1.300} & (2) \end{matrix}$ where f1 denotes a focal length of the first lens group, fw denotes a focal length of the variable magnification optical system in the wide angle end state, BFw denotes a back focus of the variable magnification optical system in the wide angle end state, and fw denotes the focal length of the variable magnification optical system in the wide angle end state.

According to the above-stated method for manufacturing the variable magnification optical system according to the present embodiment, it is possible to realize a variable magnification optical system which is, while being downsized, compatible with a large-sized imaging device, and which can attain high optical performances that various aberrations can be corrected well over from the wide angle end state to the telephoto end state and which has excellent imaging performance even upon focusing on a close distance object.

EXPLANATION OF REFERENCE SYMBOLS

-   -   G1 first lens group     -   G2 second lens group     -   G3 third lens group     -   G4 fourth lens group     -   G5 fifth lens group     -   G6 sixth lens group     -   GR rear lens group     -   S aperture stop     -   I image plane 

What is claimed is:
 1. A variable magnification optical system comprising, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a rear lens group having negative refractive power; upon varying a magnification, a distance between said first lens group and said second lens group being varied, a distance between said second lens group and said third lens group being varied, and a distance between said third lens group and said rear lens group being varied; said third lens group or said rear lens group comprising at least one lens which is moved upon carrying out focusing; and the following conditional expressions being satisfied: 0.400 < BFw/fw < 1.300 0.500 < 1/β Rw < 1.200 where BFw denotes a back focus of said variable magnification optical system in a wide angle end state, fw denotes a focal length of said variable magnification optical system in the wide angle end state, and βRw denotes a transverse magnification of a lens group disposed at the most image side in the wide angle end state, wherein a final lens group having negative refractive power is arranged at a most image side, said final lens group consists of one positive lens and one negative lens, one lens group having positive refractive power is arranged adjacent to the object side of said final lens group, and said one lens group consists of one positive lens.
 2. A variable magnification optical system according to claim 1, wherein said third lens group or said rear lens group comprises a focusing lens group which is moved upon carrying out focusing, and the following conditional expression is satisfied: 0.300 < fF/ft < 1.000 where fF denotes a focal length of said focusing lens group, and ft denotes a focal length of said variable magnification optical system in a telephoto end state.
 3. A variable magnification optical system according to claim 1, wherein the following conditional expression is satisfied: 2.00 < f 1/fw < 8.000 where f1 denotes a focal length of said first lens group.
 4. A variable magnification optical system according to claim 1, wherein the following conditional expression is satisfied: 4.000 < f 1/f 1Rw < 9.000 where f1 denotes a focal length of said first lens group, and f1Rw denotes a composite focal length of lens groups in the wide angle end state disposed on the side which is closer to the image plane than said first lens group.
 5. A variable magnification optical system according to claim 1, wherein said third lens group or said rear lens group comprises a focusing lens group which is moved upon carrying out focusing, and the following conditional expression is satisfied: 1.100 < β Fw < 2.500 where βFw denotes a transverse magnification of said focusing lens group in the wide angle end state.
 6. A variable magnification optical system according to claim 1, wherein the following conditional expression is satisfied: 0.500 < f 2fn/f 2 < 1.100 where f2fn denotes a focal length of a most object side lens component in said second lens group, and f2 denotes a focal length of said second lens group.
 7. A variable magnification optical system according to claim 1, wherein the following conditional expression is satisfied: 40.00^(∘) < ω w < 85.00^(∘) where ωw denotes a half angle of view of said variable magnification optical system in the wide angle end state.
 8. An optical apparatus comprising a variable magnification optical system according to claim
 1. 9. A variable magnification optical system according to claim 1, wherein said rear lens group comprises at least one lens group.
 10. A method for manufacturing a variable magnification optical system which comprises, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power and a rear lens group having negative refractive power; the method comprising the following steps: constructing such that, upon varying a magnification, a distance between the first lens group and the second lens group is varied, a distance between the second lens group and the third lens group is varied, and a distance between the third lens group and the rear lens group is varied; constructing such that the third lens group or the rear lens group comprises at least one lens which is moved upon carrying out focusing; and constructing such that the following conditional expressions are satisfied: 0.400 < BFw/fw < 1.300 0.500 < 1/β Rw < 1.200 where BFw denotes a back focus of the variable magnification optical system in a wide angle end state, fw denotes a focal length of the variable magnification optical system in the wide angle end state, and ßRw denotes a transverse magnification of a lens group disposed at the most image side in the wide angle end state, wherein the method further comprises one of the following features (A) or (B): (A) arranging, at a most image side, a final lens group having negative refractive power, the final lens group consisting of one positive lens and one negative lens, and arranging one lens group having positive refractive power adjacent to the object side of the final lens group, the one lens group consisting of one positive lens, (B) constructing such that the third lens group or the rear lens group comprises a lens group having positive refractive power which is moved upon carrying out focusing and consists of one positive lens.
 11. A variable magnification optical system comprising, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a rear lens group having negative refractive power; upon varying a magnification, a distance between said first lens group and said second lens group being varied, a distance between said second lens group and said third lens group being varied, and a distance between said third lens group and said rear lens group being varied; said third lens group or said rear lens group comprising at least one lens which is moved upon carrying out focusing; and the following conditional expressions being satisfied: $\begin{matrix} {0.4 < {{BFw}/{fw}} < 1.3} \\ {0.5 < {1/\beta{Rw}} < 1.2} \end{matrix}$ where BFw denotes a back focus of said variable magnification optical system in a wide angle end state, fw denotes a focal length of said variable magnification optical system in the wide angle end state, and βRw denotes a transverse magnification of a lens group disposed at the most image side in the wide angle end state; and said third lens group or said rear lens group comprises a lens group having positive refractive power which is moved upon carrying out focusing and consists of one positive lens.
 12. A variable magnification optical system according to claim 11, wherein said rear lens group comprises at least one lens group. 